I think it could make sense to implement lower-level APIs in Rust and then expose higher level APIs to JavaScript so that connections to upstream services can be shared across a pool of JavaScript Workers.
When running NodeJS at scale we had to add proxy servers to pool connections to upstream services which had been designed for smaller numbers of more highly utilized connections from large multithreaded Java application servers.
When running NodeJS at scale we had to add proxy servers to pool connections to upstream services which had been designed for smaller numbers of more highly utilized connections from large multithreaded Java application servers.